The present invention claims the benefit of Korean Patent Application No. P2002-083198 filed in Korea on Dec. 24, 2002, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method of fabricating a color filter substrate for a liquid crystal display device.
2. Discussion of the Related Art
Due to rapid development in information technology, display devices have evolved to process and display increasingly large amounts of information. Flat panel display technologies have been recently conceived and developed for display devices having small thickness, light weight, and low power consumption. Among these technologies, the liquid crystal display (LCD) device is already widely used for notebook computers, desktop monitors, and other application because of its superior resolution, color image display, and image quality.
In general, an LCD device includes an upper substrate, a lower substrate, and a liquid crystal layer disposed between the upper and lower substrates. The LCD device uses an optical anisotropy of a liquid crystal material and produces an image by varying the transmittance of light according to the arrangement of liquid crystal molecules by an electric field.
The lower substrate, which is usually referred to as an array substrate, includes thin film transistors and pixel electrodes. The lower substrate is fabricated through repeated photolithography processes to pattern a previously formed thin film. The upper substrate, which is usually referred to as a color filter substrate, includes a color filter layer for displaying color images. The color filter layer commonly includes sub-color filters of red (R), green (G), and blue (B). The color filter layer is formed by various methods including, for example, a dyeing method, an electro-deposition method, a pigment dispersion method, and a printing method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility.
FIGS. 1A to 1D are cross-sectional views showing a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art. Here, the pigment dispersion method is used.
In FIG. 1A, a black matrix 15 is formed on an insulating substrate 10 by depositing a metal material or coating a resin and patterning the metal material or the resin through a photolithography process. The black matrix 15 blocks light leakage, which is caused by irregular operation of liquid crystal molecules, in regions except pixel electrodes of an array substrate (not shown). The black matrix 15 also prevents light from going into a channel of a thin film transistor of the array substrate.
As shown in FIG. 1B, a color resist 17, which may be one of red, green and blue resists, for example a red one, is coated on the substrate 10 including the black matrix thereon by spin coating. A mask 20 having a light transmitting portion and a light blocking portion is disposed over the red resist 17, and the red resist 17 is exposed to light using the mask 20. Here, the red resist 17 is shown to have a negative property. That is, a portion of the red resist 17 that is not exposed to light is removed.
As shown in FIG. 1C, the red resist 17 of FIG. 1B is developed, and a red color filter pattern 17a is formed. Then, the red color filter pattern 17a is cured and hardened.
As shown in FIG. 1D, green and blue color filter patterns 17b and 17c are formed on the black matrix 15 through similar processes as shown in FIGS. 1B and 1C. Next, an overcoat layer 23 and a common electrode 25 are subsequently formed on the substrate 10 including the color filter patterns 17a, 17b and 17c. The overcoat layer 23 protects the color filter patterns 17a, 17b and 17c, and flattens the surface of the substrate 10 having the color filter patterns 17a, 17b and 17c. The common electrode 25 is made of a transparent conductive material, such as indium-tin-oxide and indium-zinc-oxide. The overcoat layer 23 may be omitted.
In the fabrication method of the color filter substrate using the pigment dispersion, since the color filter substrate is fabricated by repeated processes of coating, exposing, developing, and curing of a color resist, the fabrication method is complicated, thereby requiring much time and equipment. To solve the above problem, a fabrication method of a color filter substrate using thermal imaging has been proposed, as disclosed for example in U.S. Pat. No. 6,242,140.
FIGS. 2A to 2D show a method of fabricating a color filter substrate using thermal imaging according to the related art.
As shown in FIG. 2A, a black matrix 35 is formed on an insulating substrate 30 by depositing a metal material or coating a resin, and patterning the metal material or the resin by photolithography.
Then, as shown in FIG. 2B, a first color transcription film 40 is disposed over the substrate 30 including the black matrix 35. The first color transcription film 40 includes a supporting film 40a, a light-to-heat conversion (LTHC) layer 40b, and a color filter layer 40c. 
Next, as shown in FIG. 2C, the first color transcription film 40 is adhered to the substrate 30 without bubbles. A laser head 50, from which a laser beam is generated, is disposed over the first color transcription film 40. The laser beam is applied to the first color transcription film 40 in a portion where a first color filter pattern will be formed later while the laser head 50 is reciprocated in a straight line. In the first color transcription film 40 exposed to the laser beam, the LTHC layer 40b transforms light absorbed from the laser beam into thermal energy, thereby emitting thermal energy. Then, the color filter layer 40c is transferred on the substrate 30 due to the emitted thermal energy. Here, the color filter substrate may be a stripe type where color filter patterns in a line have the same color. In that case, a first line is exposed to the laser beam by moving the laser head in a straight line, but second and third lines are skipped. Similarly, a fourth line is exposed to the laser beam. In this manner, all the lines of the first color filter pattern are exposed by the above method, and the first color transcription film 40 is removed.
As shown in FIG. 2D, the first color filter pattern 45a is formed between the adjacent black matrixes 35 on the substrate 30. The first color filter pattern 45a may be a red color filter. A second color filter pattern 45b and a third color filter pattern 45c are formed through the same process shown in FIGS. 2B and 2C. The second and third color filer patterns 45b and 45c may be green and blue color filters, respectively. The substrate 30 having the color filter patterns 45a, 45b and 45c is placed in a hardening furnace, and the color filter patterns 45a, 45b and 45c are hardened. An overcoat layer 47 is formed on the color filter patterns 45a, 45b and 45c. The overcoat layer 47 protects the color filter patterns 45a, 45b and 45c and flattens the surface of the substrate 30 otherwise having steps. A common electrode 49 is formed on the overcoat layer 47 by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide.
In the thermal imaging method, manufacturing throughput of the color filter substrate is influenced by an application direction of the laser beam, wherein the laser beam is applied to the transcription film in a direction parallel to a pixel length of the LCD device. For example, in a color filter substrate of a video graphic array (VGA) LCD device, which has a resolution of 640 by 480, the VGA LCD device has sub-pixels of 640 by 3 lines (i.e., 1920 lines). Thus, the laser head 50 must scan 640 times for each color filter pattern. Therefore, total number of scans is 1920. Additionally, a size of the pixel depends on the resolution being used (e.g., VGA, SVGA (super video graphic array), XGA (extended graphic array), and so on), thereby causing difficulty to have a laser beam fit for each pixel size.
The scanning of the laser head 50 may be accomplished in a direction parallel to a pixel width of the LCD device, thereby reducing the scanning times. This may be referred to as a horizontal laser scan. The manufacturing throughput of the color filter substrate is improved due to reduction of the scanning times. However, in this case, there is a problem that scanning traces may be formed at pixel regions, thereby reducing image quality.
FIGS. 3A and 3B show a color filter substrate fabricated by a thermal imaging method using the horizontal laser scan according to the related art. FIG. 3B is an enlarged view of region A in FIG. 3A.
In FIGS. 3A and 3B, a substrate 30 includes a black matrix 35 and a color filter pattern 45 thereon. The black matrix 35 has an opening in which the color filter pattern 45 is placed. The color filter pattern 45 is formed by the thermal imaging method using a horizontal laser scan. A laser head 50 having a plurality of laser pixels 52 first scans the substrate 30 in a direction parallel to a length of a pixel P turning the laser pixel 52 repeatedly on and off. After the first scan, the laser head 50 is moved in the vertical direction of the substrate 30 in the context of the Figure by a width of the first scan, and a second scan is accomplished. Here, a scanning trace 55 is formed in a border between first and second scanning regions. The scanning trace 55 is situated on the color filter pattern 45. The scanning trace 55 on the color filter pattern 45 lowers image qualities.
Accordingly, the present invention is directed to a method of fabricating a color filter substrate for a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that reduces a total number of manufacturing processes and reduces manufacturing costs.
Another object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that improves image qualities.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of fabricating a color filter substrate for a liquid crystal display device comprises steps of forming a black matrix on a substrate; adhering a color transcription film to the substrate; disposing a laser head over the color transcription film; repeatedly scanning the color transcription film so that end lines defined by each one of the repeated scans are located on the black matrix; and removing the color transcription film so that a color filter pattern remains in color filter pattern regions defined inside the black matrix.
In another aspect, a method of fabricating a color filter substrate for a liquid crystal display device, comprises steps of forming a black matrix on a substrate, the black matrix defining a plurality of openings as color filter pattern regions; adhering a color transcription film to the substrate having the black matrix formed thereon; disposing a laser head over the color transcription film, the laser head including a plurality of laser pixels; repeatedly scanning the color transcription film by controlling ON/OFF states of the laser pixels to define an exposure pattern, wherein end lines of each one of the repeated scans is located on the black matrix; and removing the color transcription film so that a color filter pattern remains in desired ones of the color filter pattern regions.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.